For measuring an ECG of a patient, ten electrodes connected to an electrocardiograph are used as mounted at six locations for measurement of chest leads and at four locations for measurement of limb leads. Then the electrocardiograph calculates and outputs the six limb lead waveforms (I, II, III, aVR, aVL, and aVF) of the standard 12 leads and the six chest lead waveforms (V1, V2, V3, V4, V5, and V6) of the standard 12 leads, based on heart potentials detected from these ten electrodes.
In general, the relationship based on that the standard 12-lead ECG is obtained is given as described in [Table 1] below.
TABLE 1Lead I: vL − vRLead II: vF − vRLead III: vF − vLLead aVR: vR − (vL + vF)/2Lead aVL: vL − (vR + vF)/2Lead aVF: vF − (vL + vR)/2Lead V1: v1 − (vR + vL + vF)/3Lead V2: v2 − (vR + vL + vF)/3Lead V3: v3 − (vR + vL + vF)/3Lead V4: v4 − (vR + vL + vF)/3Lead V5: v5 − (vR + vL + vF)/3Lead V6: v6 − (vR + vL + vF)/3
In the above relationship, each v represents a potential detected at the electrode-mounted position.
The diagnosis of a patient's heart disease with a number of electrodes as described above can be performed in rest state in a bed of the patient as long as it is done within a fully-equipped hospital or the like.
However, for example, in cases of home and emergency medical cares, it is often the case that there is no extra room for use of many electrodes and attachment of each electrode at the appropriate position on the body surface of the living body in view of the patient's condition. Furthermore, it is sometimes difficult to transmit signals of multiple channels for acquisition of many lead waveforms. In such cases, only one channel (one lead) is commonly used to transmit the ECG signals, and the diagnosis of the heart disease is made by using at most two to four electrodes to measure some lead waveforms out of the standard 12-lead waveforms.
Under such circumstances, the inventor has developed a construction method of a standard 12-lead ECG and an ECG inspection apparatus for reconstructing the standard 12-lead ECG permitting appropriate diagnoses and treatment of various heart diseases, based on a subset of a lead system consisting of a minimum number of leads for acquisition of the conventionally known standard 12-lead ECG, and filed a patent application (cf. Patent Document 1).
Specifically, the construction method of the standard 12-lead ECG described in the above Patent Document 1 uses as the subset of the lead system consisting of the minimum number of channels, Leads I and II of the limb leads, and two leads of the chest leads, Lead V1 and, Lead V5 or Lead V6, for acquisition of the standard 12-lead ECG. Using these leads, Lead III and Leads aV (Lead aVR, Lead aVL, and Lead aVF) can be determined by an arithmetic operation based on the characteristic relationship among the leads presented in Table 1. The remaining leads of the chest leads, Lead V2, Lead V3, Lead V4, and, Lead V6 or Lead V5, can be determined by an arithmetic operation from the relationship among potentials, lead vectors, and a heart vector.
Since the standard 12-lead ECG obtained in this manner uses the subset of the lead system of the conventional standard 12-lead ECG each electrode can be mounted as readily and accurately positioned at each predetermined location and this work does not require much skill. In addition, the standard 12-lead ECG can be reconstructed with high precision, so that the diagnoses and treatment can be appropriately performed for the various heart diseases.
However, not only in the case where the standard 12-lead ECG is obtained from the six limb leads and six chest leads with the ten electrodes as before, but also in the case where the highly accurate standard 12-lead ECG is obtained by the method described in Patent Document 1 as above, it is relatively easy to confirm and diagnose an anomaly in the ECG waveforms, for example, if an occlusion of the coronary artery feeding blood to the heart muscle among the cardiac infarctions occurs in the anterior wall, the lateral wall, or the inferior wall of the heart muscle. On the contrary, if an occlusion of the coronary artery occurs at the posterior wall of the heart muscle, the electrode mounted locations are far from the posterior wall and the sensitivity of the ECG waveforms is thus too low to reflect the effect of the occlusion of the coronary artery on the ECG waveforms. In addition, the sensitivity to the right lateral wall of the heart muscle is also low because most of the electrode mounted positions of the standard 12-lead ECG are on the left side of the body surface. For this reason, it is highly likely that the occlusion of the coronary artery at the posterior wall, the right lateral wall, or the right inferior wall is overlooked in the diagnosis.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-34943
It was thus conventionally common practice to obtain an extended lead ECG using Leads V7, V8, and V9 measured at electrode mounted locations on extensions of the chest leads and/or using Leads V3R, V4R, V5R, and V6R at electrode locations symmetric with the electrode locations of the chest leads, in order to make correct diagnoses of the aforementioned posterior myocardial infarction, pulmonary heart, pulmonary embolus, right ventricular infarction, right ventricular hypertrophy, dextrocardia, other stress-related right ventricular diseases, and so on. However, the electrode mounted positions for acquisition of the extended lead ECG of Leads V7, V8, and V9 are on the patient's back or the like. The patient needs to lie back in order to be kept at rest, whereas the patient is forced into an unnatural posture in order to mount the electrodes on the patient's back or the like. In addition, there also arises a problem that the electrode mounting operation is complicated. Moreover, the ordinary standard 12-lead electrocardiographs are unable to measure the extended lead ECG of Leads V7, V8, and V9 and Leads V3R, V4R, V5R, and V6R, and there arises a need for a special electrocardiograph with an extended lead ECG measuring function having the electrodes for measurement of the extended leads.